1. Field of the Invention
The present invention relates to internal combustion engines having a charging device, e.g., a supercharger, which is outfitted with a pop-off valve.
2. Description of Related Art
Today's internal combustion engines that have an exhaust-gas driven charging device, such as a turbocharger, frequently include a so-called pop-off valve, which is situated in a pop-off pipe that bridges a compressor of the charging device. By opening the pop-off valve, a so-called pumping of the charging device may be prevented during a load change. The pumping of the charging device becomes noticeable by pulsations in a section of the air supply channel that is situated directly at the output side of the compressor, the so-called charge air line, and perhaps in the intake manifold of the internal combustion engine, and is caused by stalls at compressor blades of the compressor. Such pumping particularly occurs as a result of a pressure ratio having a higher pressure in the air supply channel and a lower pressure in the environment and at low air mass flows moved by the compressor. Furthermore, the pop-off valve may be used to avoid pressure peaks during the closing of a throttle valve situated downstream from the compressor.
The pulsations created by the pumping may lead to a considerable load on the charging device and, if they happen frequently, bearing damage on the charging device. In addition, the pumping noise represents an acoustical impairment for the passengers and the environment.
In modern engines, the pop-off valve is frequently activated by a control signal that is generated in an engine control unit, in order to open it in a specified manner when the danger of pumping exists.
If a fault occurs in the operation of the pop-off valve, such as a pop-off valve jamming in the closed state, then under certain circumstances the pumping cannot be avoided, and the danger of damage to the engine system is increased.
A method for diagnosing a pop-off valve of a charging device is known from published German patent document DE 101 11 271 A1, in which in the case of a negative load change and detected pulsations, a fault function is detected in the region of the pop-off valve. In this way it is possible to recognize a jamming pop-off valve in the closed state.
However, the method described in German patent document DE 101 11 271 A1 is not suitable for detecting a jamming pop-off valve in the open state. An pop-off valve jamming in the open state may, however, lead to the deterioration in the dynamics of the boost pressure, since a part of the volume flow required by the charging device is uselessly pumped around and around. In the worst case, this may even lead to the desired boost pressure being no longer achieved, and the boost pressure diagnosis determining a low charge fault.
In addition, in the case of an open pop-off valve, backflow in the direction of the air mass sensor and air filter may occur. Since the air mass meter, based on its construction, is usually not designed reliably to measure an air mass flow streaming out of the charge air line via the pop-off valve, this may, as a result, lead to faulty measurements of the air mass flow and faulty calculations of the mass flow into the internal combustion engine, based on the air mass flow measured faultily by the air mass meter, particularly if it is not known to the engine control unit that the pop-off valve is faultily open.